I wasted $22k on my 750i to get Dinan stage 5, the dyno result was 414WHP, my friend spent $200 on a used BMS stage 1, installed it on his 750i, and got 460whp.
After Dinan stage 5, I had lots of drive train malfunctions, so I sold the car. My friend still got his 750, and he drives it without any problems
Decision is yours to make.